Mounting structure for electrical instruments having blade terminals



Aplll 5, 1960 WALDROP 2,931,879

MOUNTING STRUCTURE FOR ELECTRICAL INSTRUMENTS HAVING BLADE TERMINALS Filed Aug. 29, 1957 2 Sheets-Sheet 1 Q INVENTOR.

Robe/ f LM/amp F. WALDROP 2,931,879

Aprll 5, 1960 R MOUNTING STRUCTURE FOR ELECTRICAL INSTRUMENTS HAVING BLADE TERMINALS 2 Sheets-Sheet 2 Filed Aug. 29, 1957 39b 29 5g 44 59!) 3.942 m a 3.9a 7 40 24 24 35 27 4/ 5'7 7 1 Q9 45 a /xa 50 aa 22 2 52 /.9

INVENTOR. Pofierf Wa/d/vp MOUNTING STRUCTURE FOR ELECTRICAL 1N- STRUMENTS HAVING BLADE TERMINALS Robert F. Waldrop, Johnson County, Kans., assignor to Milbank Manufacturing Co., Inc., Kokomo, Iud., a corporation of Indiana Application August 29, 1957, Serial No. 681,014

4 Claims. (Cl. 200-170) This invention relates generally to electrical equipment and refers more particularly to a socket for electrical instruments of the type having blade contacts and to the connection of the blade contacts with the jaw terminals of the socket.

One important object of the invention is to provide an improved socket or receptacle for use with heavy duty high capacity watt hour meters.

In the usual low capacity meter socket, as distinguished from high capacity, the connection between themeter and socket is obtained through spaced jaw terminals adapted to receive in bayonet fashion the contact blades of the meter. The jaw terminals are formed so that the'jaws will spread slightly as the blade is inserted, the material of which the jaws are composed being sufficiently resilient as to exert a clamping pressure on the opposite sides of the blade following insertion to hold the blade more or less firmly therein and at the same time establish good electrical contact.

" In sockets'for high capacity meters, however, the resiliency of the jaw material does not afford sufiicient clamping pressure against the blades as to provide a satisfactory electrical connection. As a result some means of applying additional clamping pressure to the jaws following insertion of the contact blades mustbe incorporated asa-part of the structure. It is an object of the present invention to'provide an improved arrangement for accomplishing this result.

.1- Another object of the invention is to provide amounting structure for electrical instruments of the type having blade contacts wherein means are provided for simultaneously tightening a plurality of jaws from a single source and'also wherein the tightening or clamping mechanism forms a connected part of the mounting structure. A feature of the invention in this respect resides in its incorporation in a receptacle for watt hour meters as a permanent part of the receptacle which requires no special tools for operation thereof. I

A' further object of the invention is to provide a mountingstructure of the character described wherein means are provided for electrically connecting a pair of jaw terminals to by-pass the instrument when the tightening or clamping pressure is released and to again disconnect said terminals as the tightening or clamping pressure is againapplied thereby to direct all current through the electrical instrument.

Still another object of the invention is to provide a meter 2,931,879 Patented Apr. 5, 1960 p we 4 and which have clamping means operable to increase the clamping pressure of the jaws on the blades following in-' sertion, and to maintain said pressure without relying on the inherent resiliency of the jaws.

Still another object of the invention is to provide a releasable clamping means of the character described which is positive in operation and in which the shift be- I ducting material.

tween clamping and non-clamping conditions is readily and quickly effected. v

Other and further objects of the invention together with the features of novelty appurtenant thereto will appear in the course of the following description.

In the accompanying drawings which form a part of the instant specification and are to be read in conjunction therewith and in which like reference numerals indicate like parts in the variousviews:

- Fig. 1 is a side elevation of a receptacle embodying the features of my invention, the near side wall of the receptacle having been removed and the cover not in place;

Fig. 2-is a view into the open front of the receptacle, that is, a view looking from the right hand side of Fig. 1;

- Fig. 3 is an enlargedtransverse section through themsulating block and jaw terminals taken generally along the line 33 of Fig. 2 in the direction of the arrows;

Fig. 4 is a view similar to Fig. 1 showing'the cover and a meter connected with the mounting structure; and

Fig. 5 is an enlarged perspective of the U-shaped member forming the basic element at each jaw terminal.

Referring to the drawings, reference numeral 10 indicates generally a receptacle for watt hour meters of the type for which my invention is particularly suitable. The

main body of the receptacle comprises an open front boxlike, structure preferably formed of sheet metal and having back wall'll, side walls 12, top wall 13 and bottom wall 14. As shown in Fig. 4, the front of the box is adapted to be closed by a removable cover '15 having an aperture 15a designed to fit over the enclosure of a meter. The meter has base 17 and blade contacts 18 projecting therefrom. T hecover and box arrangement may conveniently be like that disclosed in the co-pending application of William T. Martin, Serial No. 658,054. The meter is of theusual type and in the present instance will be consider'edas having four spaced blade contacts 18. I have not illustrated in detail the internal construction of the meter since such instruments are well known. Sufiice it to note that in meters of this type the upper and .lower blades respectively on opposite sides of the center are electrically connected.

Positioned within and secured to the back wall 11 of the receptacle by any suitable means is a large insulating block 19 which is constructed of any suitable non-con- Mounted on this block in a fashion later to be described are four jaw terminals 20. These socketor receptacle having clamping means of the charterminal structure wherein the individual jaws are so. spaced normally that they will freely receive the blades of the instrument while still exerting suflicient pressure on the blades as to wipe the blades as they enter the jaws terminals are positioned in accordance with the spacing of the contact blades 18 on the back of the meter and may be considered as being arranged as a left hand pair of upper and lower terminals and a right hand pair of upper and lower terminals as viewed in Fig. 2.

Each jaw terminal is identical in construction to the others, except to the extent that the upper left hand and lower right hand terminals are mirror images of the lower left hand and upper right hand terminals. The main jaw 21 of each terminal is formed as an integral part of an elongated generally U-shaped piece (detailed in Fig. 5) formed of a highly conductive material, such as copper. The web of the U-shaped piece is indicated at 22 and there are upstanding inner and outer leg portions 23 and 24 respectively. The U-shaped piece is mounted on the block 19 in a vertical groove (the base of which can be seen in broken lines in Fig. 1) formed therein with the web 22 seated against the base of the groove. Screws 25 are utilized to secure the web to the block.

'The outermost end of each U-shaped piece is fitted with a wire connector 26 adapted to receive the load or supply lines, as the case may be. In the illustrated embodiment I have provided a lay-in connector having a clamping screw 26a which can be tightened down to secure the line in place. Inthe drawing the lines 27 are the supply lines and the lines 28 the load lines. A central bus 29 is also providedin a groove running centrally of the block, this-having connections30 at its upper and lower ends. Depending on the type of meter to be used, a fifth jaw terminal 31 of the usual type may be connected with bus 29 through the medium of bracket 32 in position to receive the fifth blade of the meter (not shown). Additional jaw terminals similar to terminal 31 can, of course, beadded if necessary. However, these play no part in the invention.

As is perhaps best seen in Figs. 1 and 3, the block 19 is cut away or recessed to provide a rather large central cavity between each pair of upper and lower terminals. The base of the cavity is indicated at 33, the upper edge at 34, andthe lower edge at 35. The web 22 of, each U-shaped piece extends out over the cavity so as to provide an open space below the extending portion of the web, that is, below each jaw terminal.

The second jaw 36 of each of the jaw terminals 20 comprises the vertical leg of an L-shaped piece having a base leg 37. Leg 37 rests upon and is secured to the web 22 of the U-shaped piece by means of a shoulder screw 38 which extends through an oversized aperture in the base leg and connects with a tapped hole in the web. The smooth shank of the screw 36 is slightly longer than the thickness of leg 37 and it will thus be understood that'screw 38 serves to hold the jaw 36 to the web while still permitting slight lateral movement of the jaw relativethe web due to the oversized aperture.

Extending transversely through aligned apertures provided respectively in the main jaw 21, second jaw 36 and outer leg portion 24 of :the U-shaped piece at each jaw terminal 20 is a pin or shaft 39 that serves the dual function of thrust pin and axle. The pin is received through the apertures described in a loose fit permitting both axial and rotary movement of the pin. One end of pin 39 has an enlarged head 40 which bears against the outer surface of an outwardly bowed spring member 41 interposed between the head 40 and the outer face of the main jaw. Preferably spring 40 is a rectangular arched piece of spring steel adapted to yieldably resist drawing of the head 40 toward the main jaw 21.

Rotatably carried by the pin 39 and located on the outsideof the second jaw 36 is a camming element 42 which as viewed in Fig. 3 is of inverted U-shape with the legs -43 and 44 thereof straddling the outer leg portion 24. The rotatable mounting is effected by providing aligned apertures in the opposed legs 43 and 44, through which pin 39 extends. The element 42 is held on pin 39 by a nut 46a threaded onto the adjacent end of the pin. It will be noted that pin 39 terminates at its outer end in a reduced diameter portion 39a, thus providing a shoulder which engages the inside face of the leg 43. This accurately indexes the position of the camming ele ment on the pin so that a desired deflection of spring 41 during assembly can be obtained.

The innermost leg 44 of each camming element. is provided with a camming surface 44d which is canted from a plane normal to the axis of pin 39. This surface is arranged to bear against a boss 36a on the second jaw 36 and, as will later be described, to increase the clamping pressure of the jaws 21 and 36 on a blade contact therebetween as the camming element is rotated from one position to another.

Formed integral with the camming elements 42 of the lower jaw terminal are outwardly extending flanges 40a on which are mounted operating handles or levers 46. These levers can be attached to the flanges in any suitable fashion.

It will be noted that in the preferred embodiment as illustrated in the drawings, the upper and lower camming elements 42 on each side of the block are connected with one another for simultaneous operation. This is preferably accomplished by means of a connecting link 47 which has its opposite ends pivotally connected to the outside leg 43 of each camming member, for example, by shoulder screws '48. The link 47 is formed of a nonconductive material such as fiber board. The screws 48 are of course offset from the axis of the main thrust pin 39 so that when rotation of the lower camming element 42 is caused by manipulating lever 46 the link 47 will transmit this rotation. to the upper camming element to cause it to turn in the same direction.

I have now described in general the mechanism by which the increased clamping force at the jaw terminals is accomplished, but there are a few further points which should be noted. In Figs-1, 2 and 3 thecamming elements, jaws and operating lever on the left hand side are shown in the position which they occupy when themounting 'structure is ready for the insertion of the electrical instrument. On the other hand, the right hand terminals and camming elements are shown in the position they occupy after the instrument has been inserted and the operating lever 46 depressed to increase the clamping pressure on the contact blades. This showing is for the purpose of illustration only. It will be understood that when a meter or other instrument is to be inserted, both handles will be in the outer position represented by the left'handlever so that all jaw terminals are ready for the insertion of the blades. Following insertion, both levers are then pressed inwardly to the position illustrated by the right hand lever.

The normal condition of the jaws will thus be taken as that illustrated at the left hand side of Fig. 3. In this condition the second jaw 36 is spaced from the primary jaw 21 a distance only slightly less (for example .010 inch) than the thickness of the blade (represented fragmentarily at B) to be inserted. The lower portion of the inner face of the secondary jaw is butted against the adjacent portion of the main jaw. The length of pin 39 and the dimensions of the associated parts are such that the spring 41 exerts a pressure through camming element 42 on the secondary jaw of approximately 15 pounds (tension measured in the pin 39).

As the blade B is inserted the second jaw 36 is spread slightly away from the primary jaw, the pressure of the spring, however, resisting insertion sufiiciently to cause awiping action on the blade. This assists in obtaining firm metal to metal contact and the scraping from the blade of any foreign matter. The oversized aperture in base leg 37 of the second jaw permits the slight lateral displacement of jaw 36 that is necessary to accommodate the blade.

Once the blade B is inserted, the clamping pressure is increased by rotating the camming element 42 in a direction to increase the tension in pin 39 as earlier described.

' I have found that a final pressure of around 85 to 125 pounds (measured again as tension in pin 39) produces excellent results. The increased tension results primarily from the increase in deflection of the spring 41 as the camming element is displaced away from jaw 21 due to the relative rotation of the canted camming surface and its engagement with boss 36.

It will be observed that the leading edge of the canted surface 44a of camming element 42 terminates in a fiat portion 44b which is essentially normal to the axis of the pin. This portion may, if desired, even be canted slightlyin the opposite direction to the slant of the camming surface, or, alternatively, a depression may be formed therein. As the camming element completes its rotation, the portion 44b slides into engagement with the boss, thus relieving and eliminating any forces tending to return the cammingelement to its original position. The camming element-is thus releasably held in the second or" clamping position. To. releasevthe camming elements from the clamping position they are merely rotated in the opposite direction.

Since the camming element makes its contact with the jaw.36 substantially centrally thereof, the clamping force is app1ied to substantially the entire effective clamping area of the jaws. To increase the uniformity of clamping, the edges of jaws 36 and 21 are preferably slightly flanged as indicated to increase their structural resistance to 'flexure.

As shown in Figs. 1 and 3, the levers 46 are so oriented andof such a length that when the camming elements are in the non-clamping or normal position, the levers project beyond the forward edges of the side walls of the box. In this position they interfere with proper closing of the cover 15., It is only after the levers have been depressed and the increased clamping pressure applied that the cover can be installed. This insures against a workman failing to properly clamp the terminals before closing the unit.

In many meter installations it is desirable that an automatic by-pass be provided. The purpose of this is to prevent interruption of the supply to the customer at times when the meter is removed for inspection or repair. In its preferred form a mounting structure according to the present invention has such a by-pass and its manner of construction and operation will now be described.

Referring particularly to Figs. 2, 3 and 4, underlying the web or base portions 22 of the upper and lower terminals on each side is a jumper bar or connector 50. The upper end of each connector is secured to the under side of the upper web portion 22 as by screws 51. The other end underlies but is not secured to the lower web portion. Instead, it is resiliently urged into contact with the lower web portion by means of a leaf spring 52 which is secured also at its upper end by screws 51. A ridge or dimple 53 is formed on that side of the connector facing the lower web so as to provide better electrical contact.

Extending outwardly to one side of the lower end of the connector 50 is a flange 50a which, as shown, closely underlies the lower end of the clamp operating link 47. When the clamp operating lever 46 is in theoutward position (no clamping force applied) the link 47 is not in engagement with the flange. Thus the connector 50 electrically connects the upper and lower jaw terminals since the leaf spring 52 urges the free end into contact with the lower terminal base. However, when the lever is pushed to the second (or clamping) position, the link 47 engages the flange 50a to depress the free end of the connector and break its contact with the lower terminal. When the lever is again moved to the first position the pressure of the link on the connector is removed and the latter will returnto its circuit closing position under the influence of leaf spring 52.

From the foregoing it will be evident that the by-pass provides a means of electrically connecting the upper and lower jaw terminals 20, respectively, on the opposite sides of the structure independently of the connection through the meter. Thus if the meter is in position in the structure and steps are being taken to remove it, the by-pass will be closed as soon as the clamping force on the jaw terminals is released. The meter and its by-pass connector will be in parallel and as the meter is removed, current will continue to be delivered to the load lines. When the meter is reinstalled, the by-pass is not broken until lever 46 is again depressed and from that time on the current will flow only through the meter.

The degree of rotation permitted the camming element 42 is controlled in the present instance by so forming the operating link 47 that its upper end will strike the upper edge 34 of the block recess when the desired limit of rotation in the clamping direction is reached. When the lever is pulled out, it is eventually stopped by the lowerend of the link, striking the corresponding stop surface 53 formed atthe lower end of the recess, 1

It will be understood, of course, that the invention is not limited to a mounting structure having an auto-' matic by-pass. In certain instances such a by-pass is neither necessary nor desirable.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings it to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim:

1. A mounting structure for electrical instruments of the type having a base and at least two electrically connected contact-blades projecting therefrom, comprising a support, at least'two jaw terminals mounted on said support and positioned to receive the contact blades of the instrument, the individual cooperating jaws of the jaw terminals having a normal spacing permitting insertion of the contact blades therebetween, a pivotal lever arm mounted for rotation about an axis fixed relative said support, mechanism connected with said lever arm and operatively associated with said jaw terminals whereby to cause an increase of clamping pressure by each respective jaw terminal on the blade contact therein in response to the motion of the lever in one direction and a decrease in said clamping pressure upon movement of the lever in the opposite direction, an electrical by-pass connection between said jaw terminals, and means operated by and in response to movement of said lever and operable to interrupt said by-pass connection as said lever is moved in said one direction.

2. A receptacle for an electrical instrument of the type having a base and projecting contact blades on the base, comprising an open front box having a back wall and side walls and adapted to receive said base, an insulation block mounted on the back wall of the box, jaw terminals mounted upon said insulation block and spaced in accordance with said contact blades of the electrical instrument so that when the contact blades are aligned with the jaw terminals and the instrument is moved into the box the blades will be detachably received in the jaw terminals, a pivotal lever arm supported within said box and mounted for rotation about an axis fixed relative said box, mechanism connected with said lever arm and operatively associated with said jaw terminals whereby to cause an increase of clamping pressure by each respective jaw terminal on the blade contact therein in response to motion of the lever in one direction and a decrease in said clamping pressure upon movement of the lever in the opposite direction, an electrical by-pass connection between certain ones of. said jaw terminals, and means operated by and in response to movement of said lever arm and operable to interrupt said by-pass connection as said lever arm is moved in said one direction.

3. In a jaw terminal for receiving a contact blade, a support, a first jaw mounted on said support and having a laterally extending flange at its one edge, a second jaw resting upon said flange and so connected therewith as to have limited free movement toward and away from the first jaw, a thrust pin extending freely through aligned apertures in said jaws, retainer means connected with and preventing removal of said pin from the aperture in the first jaw in a direction toward the second jaw, said retainer means including a resilient member permitting, however, limited biased movement of said pin relative the first jaw, a rotary camming element loosely journaled on said pin outside the second jaw, second retainer means preventing movement of said camming movement axially of said pin, said camming element having a camming surface engaging the outside of said second jaw above the pin and so formed as to react with the second References-Cited in the file of this patent jaw upon rotation of the camming element in one direction to increase the tension in said thrust pinthereby to UNITED STATES PATENTS increase the clamping pressure of said jaws upon he blade 546,820 Linton Sept. 24, 1895 therebetween, and means for effecting rotation of said 5 1 532 070 Newman 'Apr. 7 192 cflmmmg element r 2,066,299 Mylius Dec. 29, 1936 4. In a aw termmal'as 1n claim 3, the inclusion on 2,118,587 Bradshaw et aL May 24, 1938 said camming surface of a section operable to stabilize 2,465,078 Fitzgerald Man 22' 1949 said camming element relative said second jaw and frictionally resist rotation of the camming element in the 10 2,654,011 Kingdon Sept 29, 1953 other direction following an increase in tension in the pin. 

